SMARCA4 (Brg) ATPase mutations induce increased occupancy and activity of Polycomb repressive factors on chromatin

We generated a library of Brg variants with mutations in conserved regions of the N-terminal ATPase domain based on mutants observed in primary tumors and cancer cell lines. Heterozygous expression of ATPase mutants leads to increased occupancy of Polycomb Repressive Complex 1 (PRC1) at bivalent CpG-island promoters. Increased PRC1 binding was accompanied by increases in H3K27me3, the mark left by the Polycomb Repressive Complex 2 (PRC2) ~2 kbp away. Overall design: Examination of PRC1 subunits Ring1b and Cbx7, PRC2 subunit Suz12, H3K27me3 in mouse embryonic stem cells expressing conditional knockout or heterozygous mutations of mSWI/SNF subunits. For both Smarca4-CreER (Smarca4flfl) and Arid1a-CreER (Arid1aflfl) conditional knockout cells, ChIP was performed 72 h after treatment with either ethanol (EtOH) or 0.8 uM 4-hydroxytamoxifen (Tam). Cells expressing V5-tagged mutants of Smarca4 (Smarca4V5) were untreated.